Many automated coffee machines in the cup-by-cup segment have the ability to prepare two cups of coffee simultaneously. Some automated coffee machines are able to produce milk froth as well in order to serve milk-based coffee drinks.
Frothing a liquid involves applying a gas like air to the liquid and mixing the liquid with the gas for obtaining bubbles in the liquid. The result is referred to as foam or froth. In many cases, the liquid to be frothed is milk. Especially in the field of making coffee and coffee specialties, there is a need for a device which is capable of frothing milk in a user-friendly manner. It is a well-known option to combine a frothing process of milk with a heating process of milk, wherein air is supplied to the milk for obtaining froth, and wherein steam is supplied to the milk for increasing the temperature of the milk.
US 2011/0072977 A1 discloses a coffee/espresso machine comprising a milk foam generating device for cappuccino. By splitting the milk foam or froth into two streams, two milk-based coffee drinks can be prepared in parallel.
In conventional devices, two streams of milk froth are obtained with one milk frothing chamber having two outlets. When a stream of milk froth is to be split there are basically two options: a pressurized piping split or an atmospheric gutter split. However, there are problems involved with these approaches.
Regarding the piping split, when a pipe (usually a silicon hose) is split into two separate pipes, the actual frothing unit can be located at a relative large distance, while the two outlets can be brought very close to the coffee outlets. An advantage of a piping split is that it enables a compact design. A disadvantage of a piping split is that cleaning of the piping split is difficult. Milk residue can lead to bacterial growth. Furthermore, milk residue can build up, (partially) clog the device and impair the quality of the milk froth.
Alternatively, an atmospheric gutter split can be used. A gutter split is known, for example from manual espresso machines, where a gutter is used for making the split of espresso. In an atmospheric gutter split, the froth to be split drops onto the gutter by gravity and is diverted to the froth outlets of the gutter by gravity as well. Thus, in addition to the height for the device for frothing the liquid, extra height is required for the atmospheric gutter split in a vertical direction between a frothing chamber of device for frothing the liquid and cups for receiving the frothed liquid. An advantage of a gutter split is that the cleaning is much easier. A disadvantage of a gutter split is that it does not allow for a compact design. As a further disadvantage the splitting accuracy is limited and is at least influenced by an accidental non-horizontal placement of the appliance. It is thus difficult to provide two streams that provide equal amounts of froth.
WO 02/21983 A1 discloses a discharge assembly for a beverage machine for preparing various beverages on the basis of coffee and/or milk, in which coffee, milk and vapor are guided to a respective discharge element via separate supply lines. Said discharge elements are disposed on support arms that form an integral part of a retainer with a central control disk and that project radially outwards. The free face of said control disk rests against the face of a stationary inlet disk, and the control disk and the inlet disk can be glidingly displaced relative to each other about their common disk axis. The control disk and the inlet disk are interspersed by channels that have two openings, the first openings being disposed on the opposite faces of the control disk and the inlet disk, and the second openings lying outside said faces. The second opening of each channel in the control disk communicates with at least one discharge element each via a tubular line and the second opening of each channel in the inlet disk communicates with one of the supply lines for coffee, milk and vapor each. The openings on the faces of the control disk and the inlet disk are disposed in such a manner that for every support arm in its discharge position the channels in the inlet disk are linked with the corresponding channels in the control disk which communicate with the discharge elements of the support arm in its discharge position.